Roy said:
There is an intereting article here about such ...Is there anything
useful you can glean from these...?
http://www.maximumpc.com/article/features/3d_showdown_8_3d_notebooks_and_monitors_reviewed
Roy
Between the GPU of the laptop and the LCD panel, they don't have to follow any public
standards for graphics. If they need extremely high bandwidth connections, they
can find a way, and not tell us how it's done. The connection from panel to
motherboard inside a laptop, is probably some variant of LVDS
(low voltage differential signaling) for example.
If you wanted to send a signal external to a computer, it is carried over
VGA, DVI, HDMI, or DisplayPort, as some examples of standards. Those are
public standards, so both senders and receivers, have to adhere to some
standard way of doing things.
The data rate necessary to carry a connection, is proportional to the
pixel dimensions of the sent signal (i.e. 1920 x 1080 = 2073600).
The third factor, is the refresh rate, or the number of times per second
the screen is redrawn. Ordinary LCD panels work at 60Hz, with technical
capability extending to 72Hz or so on cheap panels. The chemistry probably
prevents them from going much faster. 60Hz on an LCD panel, works better
than 60Hz on a CRT, due to better persistence characteristics, so 60Hz is
perfectly adequate for usage on LCD.
The 120Hz panels are another level of tech. I'm not sure what difference
exists to get to 120Hz, whether it's a more extreme form of voltage
overdrive, or different chemistry. But in any case, the display is
refreshed more frequently.
Before there was 3D on LCD, some monitors enabled 120Hz operation for the
purposes of a better quality display. There was some deal about making a
"seamless 3:2 pulldown" or some-such. 120/24FPS movies is an integer. By
interpolating frames, you get flicker free movies. This irritates some
people, and they can't stand running a 120Hz capable monitor at 120Hz
and watching movies on it. Other people love the visual effect. It's
like the difference between afternoon soap operas that are recorded
on film (flicker), versus recorded digitally on a camcorder (smooth).
A second usage for 120Hz, is for doing 3D. Using either shutter glasses,
or classical movie theater red:green glasses, you can enjoy 3D content.
OK, so where is the potential issue ? If you had an LCD monitor external to
the laptop, and it was 120Hz capable, you need enough bandwidth to
cover the width x height x refresh x bits_per_pixel.
(scroll down half way)
http://en.wikipedia.org/wiki/Hdmi
HDMI 1.4 supports 340MHz clock rates. 340MHz times 10 bits per clock, is
roughly 3400Mbit/sec on each of the red, green, and blue differential pairs
of the HDMI cabling. From that, comes the bandwidth to support
width x height x refresh etc. You need to meet the bandwidth requirement
of the display, to use that display mode.
The table on that page, claims HDMI 1.4 can support 1920×1200p60 at 48bpp.
Now, if you double the frame rate, and halve the bpp, then 1920×1200p120 at 24bpp
should be possible. 24bpp is eight bits for red, eight bits for green,
eight bits for blue, and is normal for non-dithered color LCD displays.
48bpp (high color) is overkill. Cheap LCD panels (like the one on my laptop)
are 18bpp, and temporal dither in the color space to represent in-between colors.
http://en.wikipedia.org/wiki/Dither
"Some LCDs may use temporal dithering to achieve a similar effect.
By alternating each pixel's color value rapidly between two approximate
colors in the panel's color space, a display panel which natively
supports 18-bit color (6 bits per channel) can represent a 24-bit
"true" color image (8 bits per channel)."
So sending a 3D signal from a laptop to an external monitor should be possible,
as the standard seems to have the bandwidth for it.
And as far as the laptop display itself is concerned, they can use
as many wires as it takes, to get a high bandwidth signal to the panel.
The cabling doesn't have to use HDMI, it could use some other flavor
of LVDS if required.
*******
The width x height of the panel, is an independent factor from the refresh rate.
Width x height x refresh_rate x bits_per_pixel tells you what bandwidth in
megabits per second is needed to run the display.
To give another obscure example, a certain high resolution display existed
years ago, but was not in wide circulation.
(3840×2400 IBM T220)
http://en.wikipedia.org/wiki/IBM_T220/T221_LCD_monitors
"Single, double, and quad-link support 13, 25, 41 Hz refresh rates respectively."
Some video cards, when driving something like that, use sub-60Hz refresh
rates. It means the user gets to enjoy "paper like" display quality, of
200DPI, but with motion artifacts. You can't really play games on a
display like that, because the refresh is too low.
I believe one scheme to drive that monitor, involved using four video card
outputs, each one driving a quarter of the screen. But there may also have
been attempts to drive it with a single GPU. And in that case, a much
lower refresh (GPU limited) would be used. So refresh is an independent
factor, which may be limited by the hardware to a value lower than you
might like.
But at least in my example in the previous section, it looks like HDMI 1.4
could allow something like 1920×1200p120 at 24bpp if you had an external
monitor capable of that. The GPU, the cabling/communications standard, and the
external LCD monitor, all have to support the rate, for it to work as
described.
*******
The CPU to drive such activities, is an entirely separate question.
Sure, I could use my old Celeron 300 processor, but my video or games
might only update the screen once per second. Some modern GPU chips,
have some movie decoding capabilities. So at least for movie playback,
the computing may not be done entirely on the CPU. Some of it is
done on the GPU.
To give an example of that, I did some Adobe Flash testing. On an older
version of Flash, playing a certain movie in full screen mode, takes
40% CPU. On the newest Flash, where upscaling is done on the video card
GPU, the CPU needed to play the same movie, dropped down to nothing (single
digit percentages). Depending on the situation, you don't always
need a Core i7.
HTH,
Paul
